The present invention relates generally to heat exchangers, for example tubular heat exchangers forming condensers, which are cleaned continuously by solid elements, in practice foam rubber balls, for example, systematically circulated in one of the flows concerned for this purpose.
The principle of such cleaning arrangements has been known for a very long time. See for example the documents U.S. Pat. No. 1,795,348 and DE-A-23 14 329.
When water taken from the natural environment, whether recycled or not, is passed through the tubes of exchangers, the tubes tend to become fouled. This is known in the art. The fouling takes the form of a biological surface film or deposits of fine particles or limescale, and usually a combination of these effects.
The tubes are cleaned by injecting solid cleaning elements into the upstream end of the exchanger, usually foam rubber balls whose density is substantially equal to that of the cooling water and whose diameter is very slightly greater than the inside diameter of the tubes to be cleaned.
The solid cleaning elements are captured in the outlet pipe of the exchanger by the interposition of a grid of bars, which is of elliptical form and which is inclined at an angle, for example, in the range from 20xc2x0 to 30xc2x0; the intercepted elements are rolled along the grid by the flow of water and are collected at the downstream end of the grid.
To limit the length of the device two grids in a V arrangement are often used, with the point at the top or at the bottom, with the cleaning elements respectively collected from both sides or from the center.
The elements are extracted with a small proportion of the flow of water by a pump; more generally, the control system for the solid cleaning elements includes a collection lock so that they can be stopped, allowed to circulate or changed; to recycle the solid cleaning elements, the pump feeds them, and the water, to the upstream side of the exchanger.
The grids consist of a support frame which is generally articulated to enable the grids to be pivoted and periodically cleaned by contraflow.
The frame supports the grids, which consist of equally spaced bars with gaps of a few millimeters between them.
The cleaning elements are inherently deformable and require the grids to be of very high quality: a constant spacing between the bars and freedom from asperities, discontinuities and singular points, to prevent the elements from being stopped and accumulating, which would render them inoperative.
Also, the bars must be thin to reduce the head loss.
The flow of water in the pipework, usually at a relatively high speed, of the order of 1.5 to 3 m/s, tends to generate vibrations, with potential destruction of the equipment by metal fatigue.
The current method of constructing the grids consists of drilling holes in stainless steel bars at regular intervals and assembling them by means of rods passed through the holes, with tubular spacers between the bars; these operations are time-consuming and costly; also, the durability of such grids depends on the quality of the clamping, the durability of the spacers and the spacing of the rods; what is more, it is very difficult to carry out repairs in situ in the pipe or the short pipe section in which they are mounted.
Any slight loosening is accentuated by relative movement of the elements because of the wear due to friction between the grid components and speeds up the process of deterioration. Stagnant water trapped between the rings and the rods, between the rings and the bars and elsewhere encourages corrosion of the stainless steel.
An alternative proposal is to weld the bars to support bars; this requires a very large number of welds which are very small and vulnerable to corrosion; they generate internal tensions in the metal and reduce the resistance to fatigue caused by vibration; the durability of such grids is limited.
An object of the present invention is to alleviate the above drawbacks.
In arrangements of the kind described in the document FR-A-2 716 530, for example, controlling the solid cleaning elements fundamentally entails, on the one hand, interposing on the outlet pipe of the heat exchanger an interceptor means adapted to retain the solid cleaning elements in question to prevent them being drained out to the sewer with the flow that carries them and, on the other hand, recycling the solid cleaning elements retained in this way by the interceptor means to the inlet pipe of the heat exchanger.
In practice it is also standard practice to pass the solid cleaning elements systematically through a control device adapted in particular to count them, sort them, eliminate those whose dimensions have become smaller than required, because of wear, and supply the system with the necessary new solid cleaning elements.
An object of the present invention is to propose a new interceptor grid that does not have the drawbacks of the prior art and which can be used anywhere in a control installation.
According to the invention, a grid for intercepting solid elements circulated in a heat exchanger to clean it, is characterized in that it includes a frame and molded grid members assembled onto said frame.
Advantageously, the grid members are molded from a synthetic material; the synthetic material is a polypropylene material;
Preferably, the frame is made up of metal chevrons in the form of plates disposed in a parallel arrangement with a regular pitch and transverse spacers and an articulation shaft passing through and welded to the chevrons; the grid members are substantially rectangular and extend successively between two plates.
Advantageously, each grid member has a substantially U-shaped cross section with two flanges and a core, said core is defined by a plurality of longitudinal bars joined by transverse cross members, and the bars and the cross members define a plurality of grid apertures.
Preferably, the flanges have an external longitudinal rim by means of which the grid member rests on the edge of a plates and the transverse distance of the outside faces of the flanges is equal to that between the facing inside faces of two adjacent plates between which the grid member is disposed.
Advantageously, holes in the flanges of the grid members are adapted to be aligned with bores in the plates; grid members placed on respective opposite sides of a plate are assembled thereto by nuts and bolts.
Preferably, positioning devices are provided for precise relative positioning of one grid member relative to another.
Advantageously, the positioning devices include longitudinal tongues at one end of the grid members, placed laterally at the end of the flanges and adapted to cooperate with longitudinal notches placed laterally at the other end of the adjacent grid members.
Independently of or in combination with the above features, the positioning devices include a protrusion and a recess, at one end of a grid member, disposed transversely and respectively adapted to cooperate with a recess and a protrusion disposed transversely at the other end of an adjacent grid member.
The present invention also provides a control installation for solid cleaning elements circulated in a heat exchanger to clean it, the installation including interceptor means adapted to retain and/or guide the solid cleaning elements and the installation being characterized in that the interceptor means include at least one grid as above.